Diamond core drilling is a well established drilling technique that produces a retrievable cylindrical rock core sample. The core sample is usually analyzed for content, physical and chemical properties and other attributes.
A drill including a surface mounted rotation unit rotates a diamond drill bit into a hole. Water is injected through the center of the drill rods of the drill string to cool the diamond cutter bits and flush cuttings away from the face. The exhausted water and cuttings flow around the exterior of the drill rod and up the hole.
A rock core is established by an inner tube disposed above the drill bit within the drill string. In order to retrieve the core, the inner core must be retracted from the drill string and brought to the surface without disturbing the existing drill string.
Conventionally, a wireline core barrel is disposed just upstream from the bit. The core barrel includes a spring loaded female latch facing back towards the drill rig. An overshot with a male spearhead is forced downwardly through the drill string where it mates with the latch. The entire combined core barrel and overshot are pulled up through the drill string by the wire. The core barrel is removed, the entrained core emptied and the barrel is reinserted. A new rod is threaded into the drill string; the core barrel forced back down through the drill string by hydraulic pressure; and the drilling cycle commences again.
More particularly, the conventional technique of retrieving diamond drill cores using the wireline system involves the removal and installation of a number of components. They consist of a high speed water swivel, loading chamber, overshot, wireline cable, cable packing, and water hoses. This process is time consuming, causes unnecessary wear, does not lend itself to the automation and is prone to safety hazards.
Presently, during the drilling cycle, the high speed water swivel and water hose are attached to a chuck rod and/or drill rod held by the rotation unit. This allows drilling water to be injected into the rotating drill rod string. When the drilling cycle has been completed the next operation is core recovery.
In this operation the water swivel and hose are disconnected from the rod and the hose is removed from the water swivel. The overshot with the wireline cable attached is then inserted inside the exposed end of the drill rod. The water hose (previously disconnected from the water swivel) is connected to loading chamber. The cable packing is then tightened onto the wireline cable. The water is turned on and the hydraulic pressure pushes the overshot and wireline down through the drill rods to retrieve the full core tube. When the core tube has been secured by the overshot, the cable is retracted and it pulls the core tube to the collar of the drill rods. The water hose, loading chamber, overshot, and cable are then removed from the drill rods, and the core tube taken out of the drill rods.
An empty core tube is then inserted into the drill rods, the water swivel is threaded onto the drill rod and the water hose reattached. The water is turned on and the pressure pushes the empty core tube down through the drill rods to its core receiving position. The next drilling cycle can now commence.
For various reasons, not the least of which is to provide a better working atmosphere, it is advantageous to operate the drills from a remote location rather than in a substantially closed working environment such as a mine. Considering the complexity of operating a diamond drill, a key function is the recovery of the drilled core. In addition it is advantageous to reduce the time spent on the addition and removal of parts. This in turn increases the time available for productive drilling. By eliminating the tedious job of manually continuously installing and removing components, productivity increases and safety concerns are alleviated.